Modular automotive windows produced by molding a plastic gasket directly around a piece of glass have been in commercial use since the late 1970's. Often the molded gasket can include attachment means and/or decorative trim made of plastic or metal. The first of these modular windows were produced by injection molding polyvinyl chloride directly onto the peripheral edges of the glass. Additionally, modular windows incorporating urethane gaskets molded directly on the edges of the glass using the reaction injection molding (RIM) process have seen increased usage in vehicle applications since their introduction in the mid-1980's.
All of the commercial applications to date utilize urethane or polyvinyl chloride applied to three surfaces (front, rear and side edges) of the glass for at least a portion of the total periphery of the glass. Automotive stylists continue to demand completely uninterrupted flush surfaces between the glass and sheet metal. These styling demands can be best met by molding a gasket of either polyvinyl chloride or urethane to either the back side of the glass only or to the back side and edge of the glass only.
Current commercial applications of modular windows retain the glass to the vehicle by the bond of the gasket to the glass and by physical part geometry of the gasket. With a gasket formed on three surfaces of the glass and extending around the periphery of the glass, glass retention to the vehicle could be obtained even without a bond between the glass and gasket. In fact, rear window glass of pick-up trucks have been retained in the vehicles by a separately constructed EPDM gasket that is first assembled to the glass and then assembled to the vehicle window opening without any bonding between the gasket and the glass. When properly designed, this type of installation without any bonding provides a leak free system with adequate retention of the glass to the vehicle.
However, the elimination of gasket material from the outside surface of the glass, which is required for flush installations, makes it necessary to provide other means of retaining the glass to the vehicle. One method of obtaining this retention is to form a structural adhesive bond between the glass and the vehicle sheet metal. This method has been used with many commercial applications of windshields and quarter windows. This method can be very expensive for the vehicle manufacturer since the adhesive is usually dispensed by a robot and the glass and sheet metal must each be coated with a primer or primers to promote a structural bond.
A more preferred method, especially for quarter windows, is to provide attachment and location means embedded in the window gasket such as tee studs. A sealant material such as a foam impregnated with tacky butyl rubber can be assembled to the modular window gasket by the window manufacturer providing the vehicle assembler with a low cost modular window installation. In this case, with the elimination of the gasket on the outside surface of the glass, and with the gasket mechanically attached to the vehicle, it is necessary to rely on the glass to gasket bond for complete glass retention. Failure of this bond could result in water leakage, wind noise, and possibly the separation of glass from the vehicle.
Experience with various methods of modular window manufacture focused the development efforts of this gasket to glass bond on the use of Reaction Injected Molded (RIM) urethane in conjunction with a silane based priming agent. It was felt that this technology could be developed to satisfy the bond characteristics required for flush modular windows when the gasket is only on the back side or on the backside and side edge of the glass. Urethane and silane chemistries have been used for many years as a bonding method for glass in automotive applications. Current commercial modular windows with RIM urethane gaskets use silane materials for bonding the gasket to the glass.
A description of the use of one of these types of glass priming agents is contained in U.S. Pat. No. 4,839,122. This patent describes a priming method utilizing priming agents called "Beta-seal, Glass Primer 435.18 and Beta-seal Glass Primer 435.20 produced by Essex Chemical Company. The priming method outlined in the above mentioned patent corresponds to the instructions for use provided by the manufacturer of the "Beta-Seal" material. The "Beta-seal Glass Primer 435.18" is first wiped on the edges of the glass where bonding to the gasket is required. The first primer is then coated with a second primer, "Beta-seal Glass Primer 435.20". The method then describes a waiting period of approximately twenty minutes after which the primed glass can be placed in a mold where the urethane gasket is formed directly onto the glass over the primed areas.
U.S. Pat. No. 4,761,916 describes another priming method for modular windows utilizing RIM urethane gaskets. This method uses a different "Beta-seal Glass Primer" also produced by Essex Chemical Company and designated as "Beta-seal Glass Primer 435.21". This method uses a single coat of the primer on the glass which is allowed to air dry for a minimum of two to three minutes and that the gasket must be molded onto the glass using the RIM process within thirty minutes of primer application.